No visible refraction where it should be

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Jakub Lipiński

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Aug 27, 2021, 7:31:49 AMAug 27
to astrometry

Hi!

As I want to have my astrometry in Alt Az at the end, I wanted to check how refraction affects solving. I have a 10x15 deg photo with center in ~18deg Alt (so lowest part of photo should be on ~13 deg). Accourding to wiki refraction on ~13 deg Alt should be ~5arcmins, but after solving the image with --tweak-order 1 there is no trace of refraction. I'm checking this by comparing field_x,y with index_x,y, with pixel scale of my photo ~10arsecs/pix I was expecting around 10-15 pix residuals in lower part of my photo, but there are only ~2 pix errors. How is that refraction isn't visible in those resiudals?

Dustin Lang

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Aug 27, 2021, 7:50:42 AMAug 27
to Jakub Lipiński, astrometry
Hi,
I believe --tweak-order 1 would allow a first-order "stretch" term separately in X and Y.  Try with --no-tweak?
I haven't checked, but my guess would be that the estimated pixel scale would be a compromise between the horizontal and vertical pixel scales.
cheers,
--dustin

On Fri, Aug 27, 2021 at 7:31 AM Jakub Lipiński <jlipin...@gmail.com> wrote:

Hi!

As I want to have my astrometry in Alt Az at the end, I wanted to check how refraction affects solving. I have a 10x15 deg photo with center in ~18deg Alt (so lowest part of photo should be on ~13 deg). Accourding to wiki refraction on ~13 deg Alt should be ~5arcmins, but after solving the image with --tweak-order 1 there is no trace of refraction. I'm checking this by comparing field_x,y with index_x,y, with pixel scale of my photo ~10arsecs/pix I was expecting around 10-15 pix residuals in lower part of my photo, but there are only ~2 pix errors. How is that refraction isn't visible in those resiudals?

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